Unprecedented Challenges for Fire Protection Systems
By Dr. H.C. Kung
Storage and warehouse sprinkler systems were first employed in textile mills in New England in the early 20th century as a means of protecting the equipment and textile goods stored in those early, multi-story spaces. Ceilings were low and goods were, for the most part, stored in wooden crates.
Sprinkler technology was in its infancy as a science. Later, in the 1960s, the challenge became more severe. The proliferation of plastics such as Styrofoam in packing materials and the increased use of cardboard cartons created entirely new, unprecedented challenges for fire protection systems to overcome. These lightweight storage materials allowed for storage racks to be built to greater heights and changed the dynamic of how storage spaces were designed. Taller racks create a “chimney effect” when their contents burn, creating a bigger challenge for sprinkler protection. In addition, when burned, the plastic materials now commonly used generate more heat than previous materials, increasing the fire hazard.
The scientific approach
In response, scientists and engineers at Factory Mutual began to develop a scientific approach to the evaluation of sprinkler performance in storage fire situations and to create categories of sprinklers in order to help building and fire system designers apply the proper solutions.
Throughout the 1970s and 1980s, this scientific approach yielded positive results. The prediction of a sprinkler’s response was measured in respect to the size of the fire at the time of the activation of the first sprinkler(s). The effective use of sprinkler spray was measured by its penetration ability through the fire plume. Large-scale calorimetry was used to determine the water flux required to be delivered to the top surface of rack storages of commodities of different hazard levels to achieve fire suppression.
Aided by these scientific principles, the desired effectiveness of the sprinkler could be ensured, and the quantities of water required could be optimized, resulting in cost-effective sprinkler protection of warehouses.
Key terms and concepts
Response time index (RTI): A measurement of the sprinkler response sensitivity to the gas temperature and velocity in the vicinity of the sprinkler as the fire grows enough to activate the sprinkler
Required delivery density (RDD): The water flux required to be delivered to the top surface of a burning array to achieve fire suppression or control
Actual delivery density (ADD): The water flux delivered by the sprinkler to the top surface of a burning array that actually penetrates the fire plume to attempt fire suppression or control
The application of these principles and experimental techniques led naturally to a classification of sprinkler technologies and a deeper understanding of the performance of sprinklers for protection of hazards in storage applications.
The ESFR approach
In the 1980s, Factory Mutual was leading the development of a new technology: Early Suppression Fast Response (ESFR) sprinklers. This new technology was developed to ensure a higher ADD than RDD, while providing hazard protection with storage as high as 25 feet in a 30-foot ceiling space. ESFR technology became enormously popular, protecting storage of ordinary combustibles (class 1, 2, 3 and 4 commodities and cartoned unexpanded plastic). In the 1990s, the K14 ESFR sprinkler quickly became the most popular technology for storage protection.
Beyond ESFR, storage sprinkler classification was expanded to include Control Mode (Density/Area) and Control Mode (Specific Applications). Control Mode (Density/Area) is a system design method based upon the calculation of the density of water discharged in a specified area of coverage (i.e., 0.6 gpm/sq. ft. over 3,000 sq. ft.). This approach is limited to ceiling heights of 25 feet.
Control Mode (Specific Application) sprinklers became available in a range of K11.2–K16.8 and are designed for specific water demand requirements at a pre-determined discharge pressure. Until now, this technology has been limited to 30-foot ceilings.
Recent storage sprinkler innovation
Today, system designers and contractors typically associate adequate sprinkler suppression performance of rack storage fires only with “fast response” sprinklers. Although a fast-response sprinkler responds to a fire sooner than a standard-response sprinkler, fast response alone is not the necessary and sufficient condition for a sprinkler system to achieve fire suppression. More importantly, it is the condition where ADD is greater than RDD and where superior fire suppression can be expected.
A new large K-factor standard-response sprinkler has been developed that can now achieve fire suppression of cartoned plastic commodities under a ceiling up to 40 ft high. The sprinkler model is a pendent sprinkler with a nominal one-inch diameter orifice and a K-factor of 25.2.
A series of fire tests concluded that the standard-response K 25.2 sprinkler can be as effective as ESFR sprinklers in providing protection for storages in warehouses with ceiling height up to 40 ft, since both the ESFR sprinklers and the new sprinkler were evaluated with the same fire scenarios. Based on the performance of the new sprinkler, FM Global has treated the sprinkler in the same fashion as the ESFR sprinklers, requiring a “12 head” design for the system water demand, identical hose stream demand and water supply duration. The same sprinkler installation rules with regard to physical obstructions and ceiling elements are applied to both the ESFR pendent sprinklers and the new sprinkler. However, because it does not use a fast-response link, the new sprinkler is being classified not as an ESFR sprinkler but as a CMSA sprinkler.
This type of technology can offer a significantly reduced end-head pressure as compared to traditional ESFR technology and is poised to replace ESFR as a design choice in storage applications. A benefit of the reduced end-head pressure of this new storage sprinkler is the opportunity to reduce pipe diameters in branch lines and cross mains and, potentially, even to eliminate the need for a pump, if the public water supply is strong enough, affording significant cost savings in material and labor.
Moving forward
The needs for adequate fire protection continue to grow in the storage environment as these spaces grow taller and broader and as racks are built higher. A broader variety of materials with different levels of flammability are now being stored, requiring a wider range of fire protection solutions. Complex installation guidelines for each class of sprinklers further complicate the design landscape.
In 2010, FM Global began an update of its data sheets that specifies the rules for system design and installation for storage sprinkler systems. The goal is to simplify the variations in sprinkler classes and to base the system design rules on performance of the sprinkler, not on the traditional names of the sprinkler. Hence, greater consistency in system performance can be obtained.
The fire suppression or control performance of sprinklers depends on the combined effects of the sprinkler attributes: sprinkler orientation (pendent or upright), sprinkler deflector design for generating the desirable spray pattern, volume median diameter of the spray, sprinkler sensitivity (RTI) and temperature rating. FM Global’s new data sheets base the system design rules on performance of the sprinkler rather than on the traditional name associated with the sprinkler. This sprinkler performance is predictable, based upon the parameters of the system.
As storage space design continues to evolve, new technologies continue to be introduced into the marketplace to meet increasing challenges.
Dr. H.C. Kung is the research director at Victaulic and a Fellow of the Society of Fire Protection Engineers. His career spans more than 35 years with Factory Mutual and Underwriter’s Laboratory, where he drove development of residential, quick response, ESFR, Extra Large Orifice, ESFR upright and K17 large drop sprinkler technologies.
http://www.phcnews.com/feb_11/sprinkler_feature.php
By Dr. H.C. Kung
Storage and warehouse sprinkler systems were first employed in textile mills in New England in the early 20th century as a means of protecting the equipment and textile goods stored in those early, multi-story spaces. Ceilings were low and goods were, for the most part, stored in wooden crates.
Sprinkler technology was in its infancy as a science. Later, in the 1960s, the challenge became more severe. The proliferation of plastics such as Styrofoam in packing materials and the increased use of cardboard cartons created entirely new, unprecedented challenges for fire protection systems to overcome. These lightweight storage materials allowed for storage racks to be built to greater heights and changed the dynamic of how storage spaces were designed. Taller racks create a “chimney effect” when their contents burn, creating a bigger challenge for sprinkler protection. In addition, when burned, the plastic materials now commonly used generate more heat than previous materials, increasing the fire hazard.
The scientific approach
In response, scientists and engineers at Factory Mutual began to develop a scientific approach to the evaluation of sprinkler performance in storage fire situations and to create categories of sprinklers in order to help building and fire system designers apply the proper solutions.
Throughout the 1970s and 1980s, this scientific approach yielded positive results. The prediction of a sprinkler’s response was measured in respect to the size of the fire at the time of the activation of the first sprinkler(s). The effective use of sprinkler spray was measured by its penetration ability through the fire plume. Large-scale calorimetry was used to determine the water flux required to be delivered to the top surface of rack storages of commodities of different hazard levels to achieve fire suppression.
Aided by these scientific principles, the desired effectiveness of the sprinkler could be ensured, and the quantities of water required could be optimized, resulting in cost-effective sprinkler protection of warehouses.
Key terms and concepts
Response time index (RTI): A measurement of the sprinkler response sensitivity to the gas temperature and velocity in the vicinity of the sprinkler as the fire grows enough to activate the sprinkler
Required delivery density (RDD): The water flux required to be delivered to the top surface of a burning array to achieve fire suppression or control
Actual delivery density (ADD): The water flux delivered by the sprinkler to the top surface of a burning array that actually penetrates the fire plume to attempt fire suppression or control
The application of these principles and experimental techniques led naturally to a classification of sprinkler technologies and a deeper understanding of the performance of sprinklers for protection of hazards in storage applications.
The ESFR approach
In the 1980s, Factory Mutual was leading the development of a new technology: Early Suppression Fast Response (ESFR) sprinklers. This new technology was developed to ensure a higher ADD than RDD, while providing hazard protection with storage as high as 25 feet in a 30-foot ceiling space. ESFR technology became enormously popular, protecting storage of ordinary combustibles (class 1, 2, 3 and 4 commodities and cartoned unexpanded plastic). In the 1990s, the K14 ESFR sprinkler quickly became the most popular technology for storage protection.
Beyond ESFR, storage sprinkler classification was expanded to include Control Mode (Density/Area) and Control Mode (Specific Applications). Control Mode (Density/Area) is a system design method based upon the calculation of the density of water discharged in a specified area of coverage (i.e., 0.6 gpm/sq. ft. over 3,000 sq. ft.). This approach is limited to ceiling heights of 25 feet.
Control Mode (Specific Application) sprinklers became available in a range of K11.2–K16.8 and are designed for specific water demand requirements at a pre-determined discharge pressure. Until now, this technology has been limited to 30-foot ceilings.
Recent storage sprinkler innovation
Today, system designers and contractors typically associate adequate sprinkler suppression performance of rack storage fires only with “fast response” sprinklers. Although a fast-response sprinkler responds to a fire sooner than a standard-response sprinkler, fast response alone is not the necessary and sufficient condition for a sprinkler system to achieve fire suppression. More importantly, it is the condition where ADD is greater than RDD and where superior fire suppression can be expected.
A new large K-factor standard-response sprinkler has been developed that can now achieve fire suppression of cartoned plastic commodities under a ceiling up to 40 ft high. The sprinkler model is a pendent sprinkler with a nominal one-inch diameter orifice and a K-factor of 25.2.
A series of fire tests concluded that the standard-response K 25.2 sprinkler can be as effective as ESFR sprinklers in providing protection for storages in warehouses with ceiling height up to 40 ft, since both the ESFR sprinklers and the new sprinkler were evaluated with the same fire scenarios. Based on the performance of the new sprinkler, FM Global has treated the sprinkler in the same fashion as the ESFR sprinklers, requiring a “12 head” design for the system water demand, identical hose stream demand and water supply duration. The same sprinkler installation rules with regard to physical obstructions and ceiling elements are applied to both the ESFR pendent sprinklers and the new sprinkler. However, because it does not use a fast-response link, the new sprinkler is being classified not as an ESFR sprinkler but as a CMSA sprinkler.
This type of technology can offer a significantly reduced end-head pressure as compared to traditional ESFR technology and is poised to replace ESFR as a design choice in storage applications. A benefit of the reduced end-head pressure of this new storage sprinkler is the opportunity to reduce pipe diameters in branch lines and cross mains and, potentially, even to eliminate the need for a pump, if the public water supply is strong enough, affording significant cost savings in material and labor.
Moving forward
The needs for adequate fire protection continue to grow in the storage environment as these spaces grow taller and broader and as racks are built higher. A broader variety of materials with different levels of flammability are now being stored, requiring a wider range of fire protection solutions. Complex installation guidelines for each class of sprinklers further complicate the design landscape.
In 2010, FM Global began an update of its data sheets that specifies the rules for system design and installation for storage sprinkler systems. The goal is to simplify the variations in sprinkler classes and to base the system design rules on performance of the sprinkler, not on the traditional names of the sprinkler. Hence, greater consistency in system performance can be obtained.
The fire suppression or control performance of sprinklers depends on the combined effects of the sprinkler attributes: sprinkler orientation (pendent or upright), sprinkler deflector design for generating the desirable spray pattern, volume median diameter of the spray, sprinkler sensitivity (RTI) and temperature rating. FM Global’s new data sheets base the system design rules on performance of the sprinkler rather than on the traditional name associated with the sprinkler. This sprinkler performance is predictable, based upon the parameters of the system.
As storage space design continues to evolve, new technologies continue to be introduced into the marketplace to meet increasing challenges.
Dr. H.C. Kung is the research director at Victaulic and a Fellow of the Society of Fire Protection Engineers. His career spans more than 35 years with Factory Mutual and Underwriter’s Laboratory, where he drove development of residential, quick response, ESFR, Extra Large Orifice, ESFR upright and K17 large drop sprinkler technologies.
http://www.phcnews.com/feb_11/sprinkler_feature.php
